refactor: replace legacy settings pages with redirect handlers + delete unused files

- /sites/:id/settings → redirect handler for GSC OAuth callback + deep links
- /org-settings → redirect handler for tab deep links
- Deleted: OrganizationSettings.tsx, SettingsModalWrapper.tsx, settings-modal-context.tsx

lib/settings-modal-context.tsx

@@ -1,31 +0,0 @@
-'use client'
-
-import { createContext, useContext, useState, useCallback } from 'react'
-
-interface SettingsModalContextType {
-  isOpen: boolean
-  openSettings: () => void
-  closeSettings: () => void
-}
-
-const SettingsModalContext = createContext<SettingsModalContextType>({
-  isOpen: false,
-  openSettings: () => {},
-  closeSettings: () => {},
-})
-
-export function SettingsModalProvider({ children }: { children: React.ReactNode }) {
-  const [isOpen, setIsOpen] = useState(false)
-  const openSettings = useCallback(() => setIsOpen(true), [])
-  const closeSettings = useCallback(() => setIsOpen(false), [])
-
-  return (
-    <SettingsModalContext.Provider value={{ isOpen, openSettings, closeSettings }}>
-      {children}
-    </SettingsModalContext.Provider>
-  )
-}
-
-export function useSettingsModal() {
-  return useContext(SettingsModalContext)
-}